Best reef tank heaters
Size a reef heater at 3 to 5 watts per gallon of total water, then check that the body fits the rear chamber and that the water covers it up to its MIN mark. Every heater here has a length and diameter we verified from the manufacturer's own page or manual; heaters we couldn't verify are left out.
Not sure how many watts? Use the reef heater size calculator. Own an all-in-one? Jump to your tank's heater page.
Picks
The shortest verified heater (9.57" at 25 and 50 W) with a 1.42" body that fits the rear chamber of every tank we check heaters for. Its thermal breaker cuts power if it runs dry or the water drops too low, then resets once cool.
A 1 × 1" body for narrow chambers and a simple dial. Fluval states no automatic shutoff. Keep the water between the MIN mark and the MAX line, which keeps the cap above water.
An LCD shows water temperature, and an E1 error cuts power on abnormal conditions such as low water. The smallest verified size is 100 W, which is more than 6 W per gallon on tanks under 17 gallons.
Set from your phone over the heater's own WiFi network, ±1 °F, with the same dry-run breaker as the thermocontrol. Verified sizes start at 150 W, so it suits tanks of about 25 gallons and up.
A 1" titanium element with no thermostat: it only works through an external controller, which then does all the temperature control.
Spec comparison
| Heater | Sizes | Length | Body | Thermostat | Range | Out of water |
| EHEIM thermocontrol EHEIM | 25-300 W | 9.57-19.92" | 1.42" dia | Built in | 65-93 °F, ±0.9 °F | Cuts power |
| Fluval M series Fluval | 50-300 W | 11-15" | 1 × 1" | Built in | 66-86 °F | Not stated |
| Fluval E series Fluval | 100 / 200 / 300 W | 11.75-14" | 2 × 1.25" | Built in | 68-93 °F | Cuts power |
| EHEIM thermocontrol e EHEIM | 150 / 200 / 250 / 300 W | 12.87-19.13" | 1.26" dia | Built in | 68-90 °F, ±1 °F | Cuts power |
| Titanium heater element Bulk Reef Supply | 100 / 200 / 300 / 600 W | 10.25-14" | 1" dia | None, needs controller | n/a | Not stated |
EHEIM thermocontrol
- Thermostat: Built-in adjustable thermostat (adjusting ring), control light while heating, 65-93 °F, ±0.9 °F.
- Out of water: Thermal circuit breaker switches the heater off if it runs out of water or the water is too low, and resets automatically after cooling.
- Immersion: Immerse at least to the MIN water-level mark on the heater (EHEIM publishes no numeric depth).
- Lengths converted from EHEIM's metric manual (243 mm for 25/50 W to 506 mm for 300 W); diameter 36 mm. Named here as EHEIM sells it on eheim.com.
| Watts | Length | Body |
| 25 W | 9.57" | 1.42" dia |
| 50 W | 9.57" | 1.42" dia |
| 75 W | 10.63" | 1.42" dia |
| 100 W | 12.56" | 1.42" dia |
| 125 W | 12.56" | 1.42" dia |
| 150 W | 13.58" | 1.42" dia |
| 200 W | 15.98" | 1.42" dia |
| 250 W | 17.8" | 1.42" dia |
| 300 W | 19.92" | 1.42" dia |
Sources: eheim.com (manual) · eheim.com (manual) · eheim.com
Fluval M series
- Thermostat: Built-in thermostat with a temperature dial and a pilot light while heating, 66-86 °F.
- Out of water: No automatic shutoff stated by the manufacturer.
- Immersion: Keep the water between the MIN mark and the MAX water line, so the cap stays above water.
- Fluval publishes the body as 1 x 1 in (rounded). No automatic shutoff is stated by Fluval.
| Watts | Length | Body |
| 50 W | 11" | 1 × 1" |
| 100 W | 11" | 1 × 1" |
| 150 W | 13" | 1 × 1" |
| 200 W | 13" | 1 × 1" |
| 300 W | 15" | 1 × 1" |
Sources: fluvalaquatics.com · fluvalaquatics.com · fluvalaquatics.com · fluvalaquatics.com · fluvalaquatics.com (manual) · fluvalaquatics.com (manual) · fluvalaquatics.com (manual)
Fluval E series
- Thermostat: Electronic thermostat with an LCD showing water temperature; set in 0.5-degree steps, 68-93 °F.
- Out of water: E1 error removes power to the element on abnormal conditions such as low water; unplugging resets it.
- Immersion: Fully submersible; Fluval publishes no numeric minimum depth.
- The E50 is not listed: we found no Fluval-published dimensions for it.
| Watts | Length | Body |
| 100 W | 11.75" | 2 × 1.25" |
| 200 W | 14" | 2 × 1.25" |
| 300 W | 14" | 2 × 1.25" |
Sources: fluvalaquatics.com (manual) · fluvalaquatics.com · fluvalaquatics.com
EHEIM thermocontrol e
- Thermostat: Built-in thermostat set over WiFi (the heater's own web interface, no dial), 68-90 °F, ±1 °F.
- Out of water: Thermal circuit breaker switches the heater off when it runs out of water or the water is too low, and restarts after cooling.
- Immersion: IP68, rated for permanent submersion; EHEIM publishes no numeric minimum depth.
- Only the 150-300 W sizes are listed: the manual we verified covers 150-400 W and gives no length for the 400 W.
| Watts | Length | Body |
| 150 W | 12.87" | 1.26" dia |
| 200 W | 15.19" | 1.26" dia |
| 250 W | 16.97" | 1.26" dia |
| 300 W | 19.13" | 1.26" dia |
Sources: eheim.com (manual)
Bulk Reef Supply Titanium heater element
- Thermostat: None. Bulk Reef Supply says it requires a temperature controller.
- Out of water: No automatic shutoff stated by the manufacturer.
- Immersion: Keep it fully surrounded by water, above the minimum immersion marker; it can be damaged otherwise.
- IP68 titanium element. Use it on a GFCI outlet and through a controller.
| Watts | Length | Body |
| 100 W | 10.25" | 1" dia |
| 200 W | 10.25" | 1" dia |
| 300 W | 10.25" | 1" dia |
| 600 W | 14" | 1" dia |
Sources: brsinstructions.s3.amazonaws.com (manual) · bulkreefsupply.com
Heater controllers
A heater stuck on can cook a tank. Plug the heater into a controller set 1 to 2 °F above the heater's own setting, so the controller only cuts power if the heater fails. A heater with no thermostat, like the Bulk Reef Supply element, needs a controller to work at all.
Innovative Marine Helio Universal Controller
- External controller with a titanium remote sensor.
- Rated 1000 W per the manual
- Accuracy better than +/-1 F
- High and low temperature alarms
- Cuts power and alarms when the controller and sensor readings disagree
- Set range 59-95 F. Bulk Reef Supply bundles this controller with its titanium element.
Sources: innovative-marine.com · brsinstructions.s3.amazonaws.com (manual)
Inkbird ITC-306T
- Plug-in temperature controller with a probe; switches the heater outlet on and off.
- Heating only
- 10 A max at 100-240 V
- High and low temperature alarms
- Probe fault alarm
- Inkbird rates it in amps (10 A), not watts.
Sources: inkbird.com · inkbird.com
Heaters by tank
Each page checks every heater above against that tank's rear chamber: body width, length against the assumed water depth, and wattage.
FAQ
What is the best heater for a reef tank?
One sized at 3 to 5 watts per gallon of total water that fits where it goes, plus a controller as a backstop. For nano all-in-one tanks the EHEIM thermocontrol stands out in our verified list: it is the shortest at 25 and 50 W and it cuts power if it runs dry.
Do titanium heaters need a controller?
The Bulk Reef Supply titanium element does: it has no thermostat, so the controller switches it on and off. Heaters with a built-in thermostat work alone, but a controller is still cheap insurance against one sticking on.
Why are some popular heaters missing?
We list a heater only when its manufacturer publishes the length, diameter and thermostat details our fit checks need. Heaters we could not verify from manufacturer sources are left out until we can.
Specs from manufacturer pages and manuals, verified 2026-10-19. No prices are listed; check the retailer for current pricing.